Gerry Giggins: How to hit the sweet spot when deciding on the best time to harvest first cut silage

Silage cutting dates should be determined by the sugar levels present in the grass leaf, says Gerry Giggins PHOTO: DAMIEN EAGERS

Gerry Giggins

April 29 2021 06:49 AM

We have had a late spring on the grass growth front and the usual scenario of cutting excess grass to make bales is a rare sight this year.

Dry and cold weather has affected soil temperatures, fertiliser uptake and grass growth rates. This has affected grazing management on many farms, with supplementary feeding required to extend grass supply in some cases.

Silage harvest dates will also be affected, with many farms now having to revise their targeted cutting date.

Grazed grass is a beef farm’s cheapest feed source and next to this is good quality grass silage. Just as improved grassland management and grazing techniques result in better animal performance and lower costs, the same applies to the silage making and management process.

When winter arrives, the more high-quality forage we can feed to animals, the healthier they will be and the lower the overall feeding costs are.

The cost of making silage will increase this year due to higher input costs. However, at a cost of €120-€140 per tonne, dry matter, high quality grass silage represents excellent value in comparison to concentrate costs of €250-€300 per tonne dry matter.

It costs the same to make a tonne of good or bad quality silage, but the cost of supplementing these different silages at feedout will vary greatly.

There are many factors that will play a role in determining the final quality of grass silage.

While weather around the time of harvest is sometimes seen as the main impact on silage quality, there are many other issues that can influence the final quality.

Quality

Silage quality is directly linked with the stage of growth at which the grass plant is harvested.

Excess dead leaf material from the previous season’s growth will dilute the quality. Silage ground should be grazed correctly or in some cases zero-grazed either late in the season or in early spring to remove any dead material or over wintered growth.

Obviously, care should be taken to avoid poaching and damage to soil structure during the grazing/ zero grazing process.

Having silage ground stripped bare allows for a blank canvas of new grass growth to occur, increasing the quality of the sward for harvest.

In most cases this year, slurry was applied in ideal conditions i.e. in dry weather and with little damage caused to fields.

Unfortunately, the subsequent low rainfall in many parts have resulted in slurry residue still remaining visible on fields.

This is particularly noticeable where dribble bar and trailing shoe spreading were used.

The base of the grass plant should be assessed prior to harvest to determine whether any slurry residue is remaining. Where such residue makes its way back into the silage pit, fermentation will be negatively impacted.

It will also increase the ash content of the silage and has the potential to lock up vital mineral availability.

Soil contamination will have a similar effect to that of slurry contamination. Mowing height, setting of the tedder/ rake and harvester pick-up all need to be correctly aligned to ensure minimal amounts of soil contamination.

Grass is converted to silage once it undergoes the fermentation process. The aim is to have this fermentation process occur as quickly as possible to reduce any losses or composting.

In Ireland, harvest date is generally determined by the nitrogen application date and waiting for six to eight weeks growth.

Sugar levels

I feel the cutting date should be determined by the sugar levels present in the grass leaf.

For example, after five to six weeks of spring growth post-fertiliser spreading, the grass plant will still have nitrogen present but if sugar levels are high and weather conditions are favourable, I would encourage harvesting.

Sugar levels on a sunny day can vary greatly, from 2-4pc in the morning, to an afternoon/ evening peal of 8-12%.

In my experience, wilting can play a major role in either enhancing or negatively impacting silage quality. There is a fine line between the requirement to wilt grass and for how long.

Where grass is mown dry, with high sugar levels in the leaf, excess drying of the plant won’t improve fermentation.

As with all farm activities, reducing waste is of upmost importance. Proper compacting and covering of the pit is essential.

Expelling air from the grass clamp will aid the fermentation process and stability of the clamp greatly. I am sometimes worried by the lack of compaction that takes place on silage pits.

Even an extra hour of compaction will greatly improve ensilability. Surfaces of the pit that are difficult to compact would benefit from
the application of salt to aid preservation.

Covering the pit should occur as soon as compaction is finished. Oxygen barrier sheets will greatly reduce surface air contact and will result in very little silage wastage when used in conjunction with heavy duty covers and correct weighting.

Gerry Giggins is an animal nutritionist based in Co Louth